1. Field of the Invention
The present invention relates to a probe for an oxymeter of the reflection type which measures a blood oxygen saturation of a subject based on lights which are reflected from skin of the subject, and more particularly to such a probe which is adapted to be set on the skin.
2. Related Art Statement
There is known a probe for a reflection-type oxymeter which measures a blood oxygen saturation of a subject, which probe includes (a) light emitting means for emitting two lights having different wavelengths toward skin of the subject, (b) light detecting means for detecting the lights reflected from the skin, and (c) a housing accommodating the light emitting and detecting means. For example, such a probe is disclosed in U.S. Pat. No. 4,880,304. The prior art probe is set on the skin with, for example, a pressure sensitive adhesive tape being applied over both the housing and the skin.
The light emitting means of the above indicated reflection-type oxymeter emits an infra-red light and a red light having different wavelengths, toward the skin, and the light detecting means detects the lights reflected from the capillary bed in the hypodermis lying under the epidermis. The oxymeter determines a blood oxygen saturation of the subject based on the amplitudes of intensities of the lights detected by the light detecting means, according to a predetermined relationship (formulae). However, since the prior art probe is set on the skin by being pressed against the skin with an adhesive tape being applied over both the housing and the skin, the pressing force applied to the probe or housing may largely vary in different cases, thereby deteriorating the reliability or accuracy of blood oxygen saturation measurement. As clearly shown in the graph of FIG. 3, the intensity of a light reflected from the skin of a subject varies depending upon the pressing force applied to the housing or skin. The prior art probe suffers from the problem that the pressing force applied to the housing for setting the housing on the skin of the subject, largely varies because of the application of an adhesive tape over both the housing and the skin and therefore does not always fall within a suitable range. In the case where the pressing force applied to the probe exceeds the upper limit of the suitable range or does not reach the lower limit of the range, the light reflected from the skin shows an insufficient intensity to be utilized for determining a blood oxygen saturation.